Surface coated propellent explosive powders



Patented Sept. 17, 1%46 UNI SURFACE COATED PROPELLENT EXPLOSIVE POWDERS Thomas Thomson, Kilmarnock, Scotland, assignor to Imperial Chemical Industries Limited, a corporation of Great Britain No Drawing. Application July 15, 1943, Serial N 0. 494,833. In Great Britain August 19, 1942 6 Claims.

The present invention relates to an improved method of preparing progressive burning surface coated single base smokeless powders, especially for use in rifles and machine guns, and relates more particularly to an improved method of coating smokeless powder in the form of base grains with a deterrent and applying the graphite glaze that is useful for coating flake as well as other grain forms.

It is well known that the burning speed of smokeless powder grains can be modified by coating them with a deterrent material so that a high velocity of the projectile can be maintained up the barrel without excessively high breech pressures, and the resulting powders are often referredto as progressive burning powders. The manufacture of progressive burning powders of this kind, especially those of flake form, by the coating methods hitherto in use has, however, suffered from certain inconveniences or disadvantages.

According to the usual practice, for instance, the powder grains are tumbled with the deterrent in a rotating pan into which steam is injected, and the product is then steeped in hot water, stoved and glazed. In order to fix the deterrent firmly in the superficial portion of each grain it is necessary to steep the coated grains in the hot water for a long time, for instance 24 hours. In the case of flake powders it is the practice after stoving to subject the coated grains to an additional tumbling treatment with alcohol that is designed to modify the contours of the individual grains and thus enable a product of higher bulk density to be obtained than would otherwise be the case. In this case the glazing operation may be combined with the alcohol treatment by introducing at least a portion of the graphite at some suitable stage into the powder before the complete evaporation of the alcohol. Advantageously some of the graphite is present when the dry powder is introduced into the vessel in which the alcohol treatment is to take place. After glazing the alcohol treated powder is again stoved, and is rehumidified.

It is not usually practicable to apply the deterrent in alcoholic solution since in the case of some deterrrents the solubility of the deterrent in alcohol is inconveniently low and in the case of others the powder grains are rendered so sticky when the deterrent is used in alcoholic solution that the dried grains tend to adhere to one another and therefore run badly and fail to assume a satisfactorily high bulk density.

It is an object of the present invention to provide a simplified method for the preparation of a deterrent coated smokeless powder. It is in particular an object of the invention to provide a method for the production of a deterrent coated smokeless powder of good running properties whereby the necessity for steeping in hot water is avoided and whereby the treatment with the deterrent and the graphiting are carried out in a single operation. It is also an object of the invention to provide a progressive burning flake smokeless powder of satisfactorily high bulk density and other desirable properties.

According to the present invention the base rain powder is surface coated with a deterrent by tumbling it with an alcoholic solution of a solid deterrent which has good solubility in alco- 1101 and which has weak gelatinizing power for nitrocellulose. As deterrrents which satisfy these criteria and which may be used according .to the present invention there are pentaerythritol tetraacetate and phthalide.

The present invention is based upon the unexpected discovery that there is a limited class of deterrents which, unlike other deterrents, have a sufficiently good solubility in alcohol to permit of their being applied to the grains in the form of an alcoholic solution without rendering the grains so sticky that they adhere to one another after drying and therefore run badly and do not assume a satisfactorily high bulk density,

The tumbling operation is suitably conducted in a vessel which can be closed at the commencement of the operation and opened when the treatment is partially completed so that the alcohol is then allowed to evaporate. In putting the invention into effect, the graphite glazing treatment may be combined with the treatment with .the alcoholic solution of pentaerythritol tetraacetate or phthalide. This may be accomplished, for example, by tumbling the stoved base grain powder with the alcoholic solution in the presence of at least some of the graphite, and intro- 3 Example 1 1000 parts of flake nitrocellulose powder of thickness 0.012 inch and side of square 0.045 inch, an equal weight of lignum vitae balls, and 2.5 parts graphite were put in a rotatable copper pan heated to 45 C. and the pan was run for 2 to 3 minutes. A solution of 60 parts pentaerythritol tetra-acetate in 100 parts alcohol was next run into the pan, which was then closed and rotated for half an hour. The cover of the pan was then opened and the pan was run open until the powder had dried oir somewhat and was running freely. 7.5 parts graphite were then added to the resulting coated powder and the pan was closed and rotated for a further two hours. The powder was discharged and stoved for three days at 43 C. and conditioned for moisture content in the usual way.

The satisfactory ballistics of the resulting coated powder are illustrated in the following figures obtained on firing it in ammunition for a 7 mm. Mauser rifle:

The charge weight required to give a muzzle velocity of 2818 feet per second was 47.0 grains, and the pressure attained was 18.17 tons per square inch. When a flake powder of the same dimensions and interior composition coated in the usual manner with symmetrical dimethyldiphenyl-urea was tested at the same time it required a charge weight of 48.5 grains to give a velocity of 2789 feet per second, and produced a pressure of 18.04 tons per square inch.

Example 2 The manufacture was carried out precisely as in Example 1 except that a solution of 70 parts phthalide in 100 parts alcohol was employed instead of a solution of 60 parts pentaerythritol tetra-acetate in 100 parts alcohol.

When fired in ammunition for a 7 mm. Mauser rifle a charge of 47.0 grains of the glazed coated powder made according to Example 2 was required to give a muzzle velocity of 2,801 feet per second and the pressure attained was 17.92 tons per squar inch. When fired at the same time the glazed powder coated with symmetrical dimethyl-diphenyl-urea mentioned in Example 1 required a charge weight of 48.5 grains to give a muzzle velocity of 2776 feet per second, the pressure attained being 17.58 tons per square inch.

I claim:

1. A process for the treatment of single base smokeless powders which comprises tumbling the base grain powder with an alcoholic solution of a solid deterrent which has good solubility in alcohol and which has weak gelatinizing power selected from the group consisting of pentaerythritol tetra-acetate and phthalide.

2. A process as claimed in claim 1 in which the tumblin operation is conducted at a raised temperature below the boiling point of alcohol.

3. A process for the treatment of single base smokeless powders which comprises tumbling the base grain powder With an alcoholic solution of a solid deterrent which has good solubility in alcohol and which has weak gelatinizing power selected from the group consisting of pentaerythritol tetra-acetate and phthalide, and glazing the grains with graphite.

4. A process as claimed in claim 3 in which the stoved base grain powder is tumbled with the alcoholic solution of the deterrent in presence of at least a portion of the graphite required for the glazing operation.

5. A process for the treatment of single base smokeless powders which comprises introducing into a tumbling vessel the stoved base grain powder and a portion of the graphite normally used for glazing the grain powder, thereafter adding to the vessel an alcoholic solution of a solid deterrent which has good solubility in alcohol and which has weak gelatinizing power selected from the group consisting of pentaerythritol tetraacetate and phthalide, tumbling the contents of the vessel, adding the remainder of the graphite normally required for the glazing of the grain powder, and continuing the tumbling operation under conditions permitting of the evaporation of the alcohol.

6. A process for the treatment of single base smokeless powders which comprises tumbling the base grain powder with an alcoholic solution of a solid deterrent which has good solubility in alcohol and which has weak gelatinizing power selected from the group consisting of pentaerythritol tetra-acetate and phthalide, glazing the grains with graphite, and, subsequent to the tumbling and glazing operations, stoving and humidifying the treated grain powder.

THOMAS THOMSON. 

